1. Technical Field
A technique disclosed in this specification relates to an electric vehicle. The electric vehicle referred in this specification means a vehicle that includes a motor for traveling (traveling motor) for rotating drive wheels. The electric vehicle includes: a vehicle that includes an engine in addition to the traveling motor (a so-called hybrid vehicle); a vehicle that supplies electric power from a battery to the traveling motor; and a vehicle that supplies the electric power from a fuel cell to the traveling motor (a so-called fuel cell vehicle).
2. Description of Related Art
In Japanese Patent Application Publication No. 2014-124045 (JP 2014-124045 A), a hybrid vehicle in which drive wheels are rotated by an engine and a traveling motor is disclosed. A circuit for driving the traveling motor has: a boosting converter that increases a direct current voltage of a battery; an inverter that converts an output voltage of the boosting converter to an alternative current voltage and supplies the alternative current voltage to the traveling motor; and a motor control unit (an MG-ECU) that controls the boosting converter and the inverter. A smoothing capacitor for suppressing pulsations of a voltage is connected between input terminals of the inverter (that is, between output terminals of the boosting converter). In a normal state, a high voltage is applied to the smoothing capacitor. Thus, at a time of abnormality, electric charge needs to be discharged from the smoothing capacitor to secure safety. For this reason, this hybrid vehicle has a discharge circuit for discharging the electric charge of the smoothing capacitor, and the motor control unit controls the discharge circuit. This hybrid vehicle also has: a main control unit (an HV-ECU) for controlling output distribution of the engine and the traveling motor; and a crash possibility determination unit (a PCS-ECU) for determining a possibility of a crash of the vehicle.
In electric vehicles including the above-described hybrid vehicle, in order to secure the safety, it is demanded to promptly discharge electric charge of the smoothing capacitor during a crash. In the hybrid vehicle of JP 2014-124045 A, the discharge circuit discharges the electric charge of the smoothing capacitor during the crash. Note that, because a large current flows through the discharge circuit during an operation of the discharge circuit, a significantly large load is applied to components that constitute the discharge circuit. Thus, the discharge circuit cannot be operated frequently. Therefore, it becomes necessary to accurately detect the crash of the vehicle and to operate the discharge circuit only when necessary.
In the hybrid vehicle of JP 2014-124045 A, a crash possibility determination and a communication disruption determination are combined to detect the crash of the vehicle.
The crash possibility determination is made by the crash possibility determination unit. The crash possibility determination unit is connected to a sensor group that is mounted in the vehicle. The sensor group is constructed with plural sensors that measure a travel state of the vehicle (a situation around the vehicle, a vehicle speed, a vehicle route, and the like). For example, the sensor group possibly contains: a millimeter wave radar and/or a camera that detects obstacles and other vehicles around the vehicle; an acceleration sensor that detects acceleration added to the vehicle; a vehicle speed sensor that detects a travel speed of the vehicle; an angular sensor that detects a steering angle of a steering wheel; and the like. Prior to the crash, the crash possibility determination unit determines whether there is a possibility of the crash of the vehicle based on data output by the sensor group. If there is the possibility of the crash of the vehicle, the crash possibility determination unit transmits a signal indicative of such a fact to the motor control unit. Even if it is determined that there is the possibility of the crash, the crash may be avoided by means of emergency avoidance or the like. Thus, it is not adequate to determine, only by the crash possibility determination, that the crash has occurred.
The communication disruption determination is made by the motor control unit. The main control unit is configured to periodically transmit a signal (for example, a signal for controlling the traveling motor, and the like) to the motor control unit. On the basis of the periodical signal transmitted by the main control unit, the motor control unit repeatedly determines whether communication with the main control unit is disrupted. There is a case where the communication is disrupted due to failure of the main control unit, a communication wire, or the like. There is also a case where the communication is disrupted due to the crash of the vehicle. Thus, it is not adequate to determine that the crash has occurred only by the communication disruption determination.
Accordingly, the motor control unit of JP 2014-124045 A determines that the vehicle has crashed in the cases where it is determined that there is the possibility of the crash by the crash possibility determination and where it is determined that the communication is disrupted by the communication disruption determination. A situation, in which the communication is disrupted in a state where there is the possibility of the crash of the vehicle, means that a possibility that the vehicle has crashed is high. By combining the crash possibility determination and the communication disruption determination, it becomes possible to accurately grasp the crash of the vehicle. Note that, in this hybrid vehicle, the motor control unit can detect the crash even when the communication between the main control unit and the motor control unit is disrupted by the crash. Thus, even when the above communication is disrupted during the crash, the electric charge can be discharged from the smoothing capacitor.
In the hybrid vehicle of JP 2014-124045 A, the following processing is executed prior to electric discharge of the smoothing capacitor. First, prior to the crash, it is determined that there is the possibility of the crash of the vehicle by the crash possibility determination. In addition, in parallel with the crash possibility determination or after the crash possibility determination, the communication disruption determination is made. A certain time is required for the communication disruption determination because the communication disruption determination is made by monitoring the periodical signals for plural intervals. In the case where the vehicle crashes during or before the communication disruption determination, the periodical signal is no longer transmitted to the motor control unit. The communication disruption determination is finished after the crash, and it is then determined that the communication is disrupted. At this stage, the electric charge is discharged from the smoothing capacitor. The electric charge is discharged from the smoothing capacitor at such timing that is delayed by the time required for the communication disruption determination from the crash. In order to further improve the safety, a technique for advancing electric discharge timing of the smoothing capacitor is necessary.